1. Field of the Invention
My invention generally relates to the field of the handling and consolidation of spent nuclear fuel rods and, more particularly, to a method of improving the geometric utilization of the interior of a cylindrical container for the storing, shipping and/or disposing of such spent nuclear fuel rods.
2. Description of the Prior Art
Presently, nuclear fuel assemblies, of square cross section and containing spent nuclear fuel rods, are placed in fuel racks which are stored under water in storage pools. When a pool reaches its storage capacity, or at any other desired time, the individual spent fuel rods are removed from a fuel assembly and re-inserted and consolidated in long cans which have the same square cross section as one original fuel assembly. Each square can normally contains the fuel rods from two of the original spent fuel assemblies from either a pressurized water reactor (PWR) or a boiling water reactor (BWR).
Once the spent fuel is finally removed from the fuel storage pool for possible on-site storage, transport off-site, possible interim storage and retransport, and ultimate delivery to a repository or a reprocessing plant, the square cans of consolidated fuel rods are placed in (shielded) casks or other containers which have a cylindrical geometry and a circular cross section (see FIGS. 1B and 2B). Since these square cans have the same cross sectional area and dimensions as the original fuel assemblies which they replaced in the fuel racks in the storage pool, these square cans will normally not fit very efficiently in the containers or casks which are of circular cross section (see FIGS. 1B and 2B). Thus, there exists the problem of trying to improve the geometric efficiency with which square cans of consolidated fuel rods fill the containers of cylindrical volume and circular cross section.
The following U.S. patents may be relevant prior art with respect to my invention: Nos. 3,731,101; 3,859,533; 4,042,828; 4,063,999; 4,171,002; 4,242,178; 4,366,115; 4,399,366; and 4,447,729.
Pat. No. 3,731,101 discloses a solution to a related problem, whereby there is provided a (shielded) "cask" having three curved walls to produce a (shielded) cask having a generally rounded triangular cross section, the result being a (shielded) shipping container having a maximum capacity for spent fuel elements while having a minimum amount of weight. The shipping container shown in FIG. 3 has an inner shell defining a fuel element cavity with a cross-sectional configuration bounded by the three curved walls. The fuel elements are separated by spacers.
Pat. No. 4,063,999 achieves vertical staggering of active fuel sections by spacer plates as seen in FIG. 6.
Pat. No. 4,242,178 discloses an unshielded storage drum for the temporary storage of bent spent fuel rods.
Pat. Nos. 4,171,002 and 4,399,366 disclose shielded cylindrical shipping containers (a transport "flask" and a shipping "cask", respectively) for radioactive material and having square shaped compartments for holding spent fuel rods; however, neither of these patents addresses the question of geometrically improving the occupancy efficiency of a cylindrical container for spent fuel rods. The remaining patents are of background interest.
Pat. No. 4,447,729 discloses a shielded cylindrical container for the transportation of irradiated reactor elements.